The present invention relates generally to ink-jet printing and deals more particularly with an ink-jet positioning apparatus or circuit and a related method for maintaining a desired spacing between an ink-jet printing means and a receiving surface.
Ink-jet printing devices such as, for example, non-impact matrix printers and the like, print alphanumeric characters, graphics or other such displays by generally ejecting ink drops or dots onto a receiving surface in accordance with control information provided to operate an ink-jet printing head. Generally, the receiving surface is held stationary against a back support or other means relative to the printing head to maintain a constant spacing between the head and the surface. As the printer head moves along a scan line it moves past a succession of points on the line in relation to each of which the printer head may eject an ink drop which lands on and prints a dot at that position. The flight of an ink drop in such ink-jet printing devices where a constant spacing is maintained between the ink-jet head and a receiving surface is at a fixed, uniform trajectory for each dot printed. Such ink-jet printing devices are commonly know in the art.
The recording medium forming the receiving surface used in such printing devices is generally of a uniform thickness and structurally undistorted so that there is no variation in the spacing between the ink-jet printing head and the surface along a line scanned by the head. Consequently, the ink-jet printing head in these devices can be positioned closely to the receiving surface and once positioned are able to maintain the desired spacing without additional adjustment during the printing process.
In some graphics display generating devices such as, for example, large scale sign generators for printing roadside billboards and the like, ink-jet printing techniques are used to produce a desired sign or other display. In one such large scale sign generator, panels used as the recording medium are placed in a side-to-side abutting relationship and pass in endless conveyor fashion by a dot printing mechanism which applies dots onto the face or receiving surface of the panels in a scanning fashion to produce the desired display. Often times the panels used as the recording medium are warped or have other structural distortions affecting the uniformity of the receiving surface. Such warped panels cause the spacing between the ink-jet printing head and the receiving surface to vary from a preset or desired spacing as the panels move by the dot applying station.
If the spacing increases placing the receiving surface too far from the printing head, the ejected ink drops start to drop before landing on the surface. Consequently, dots applied to a succession of points along a line on a warped receiving surface print a wavy or irregular line rather than a straight line. If the spacing becomes to small, the receiving surface is brought into contact with the printing mechanism causing damage to the ink-jet printing head. It would therefore be desireable to have a continuously variable positioning ink-jet printing head to compensate for movement of the receiving surface toward and away from the printing head to maintain a constant spacing between the receiving surface and the printing head at the printing location for each printing location.
It is therefore a general aim of the present invention to provide positioning apparatus for maintaining a desired spacing between an associated ink-jet printing head and a receiving surface at a printing location.
Other features and advantages of the present invention will become readily apparent from the following written description and the drawings forming a part thereof.